Part 3 of 3 of my long post. More E28 look-for's:

6) Driveline

• Check guibo, the rubber flexdisk connecting the output of the tranny to the driveline. At 100K it will be cracked, and may be the cause of a shudder at certain speeds (frequently 25 to 35 mph), especially while under load.
• Ditto the center bearing and support, but much harder to check, as you have to dispose of the exhaust system (well, remove enough to get the heat shield off, but you know what I mean!).
• Do the traditional twist-drive-components-and-note-any-play of the two U-joints. The rear one is the more likely to fail, and is easily observed. Bear in mind that if they are bad, you will need to get the driveline rebuilt, $450ish if you rebuild the whole thing (recommended). 7) Suspension, Steering and Brakes
• There are books written on the subject of the front control arms, but the exec summary is: they all die. Symptoms of impending doom are shuddering when braking, especially from say 65 down to 45. May get very jumpy at the steering wheel. There are upper and lower control arm bushings and ball joints, and lots of alternatives (bushing upgrades, etc.). FAQ's abound. $160-$800 in parts.
• And, of course, the front rotors warp. $120ish. Always replace the 5mm hex that secures the rotors. Cheap insurance.
• The 535i boost system feels weird (the 528e is a very vanilla vacuum boost.) The point is; in a perfectly healthy hydralicboosted system, you can 'surprise' the system if the engine is running but the car is standing still by stomping the brake pedal hard - you can make it most of the way to the floor. Not to worry; you are 'way past the point that triggers ABS, but tech checks for track days may be tricky - the typical M3 driver doing the check will panic. Explain ahead of time!
• With the engine running for brake boost, stand on the brake pedal for 30 seconds or so. If it drifts toward the floor, time for a master cylinder. Replace, don't rebuild. $80 to $180, +/- year and/or ABS.
• Steering should be 'tight' when gently rocked at the center of travel when the engine is off. 'Clunks' may mean Pitman arm bushings (_bad_), loose collar nut under dash (easy) or bad center track rod (cheap, <$60, but obnoxious).
• The two senders on the brake pressure regulator regularly leak. Replace them both, $32ish.
• There is a 'nitrogen ball', frequently referred to as the 'brake bomb', due to it's cartoon-bomblike appearance, that dies. Symptom is a slow-to-respond brake pedal, frequently accompanied by a flash of the 'brake' idiot light, and/or no brake boost immediately after shutting down the engine. (It should give several-to-many 'assists' after shutdown). Again, several fine FAQ's on replacement (somewhere). $60ish.
• When checking the p/s and brake boost fluid level, bear in mind that if the engine has been running and the nitrogen ball is in working order, there is a inch or so of fluid in the ball. Fully discharge the ball by stomping the brake pedal 10-20 times and watch the fluid level creep up. Adjust to the line in the side of the can at that point. This applies to the 'i' only; as the 'e' uses vacuum boost.
• Fluid should be pretty; not black. There is a filter in the bottom of the reserviour that should be changed on the 'i'. 8) Interior, Electrical
• Alternator brushes ($5.50 at BavAuto) are typical 140K items. Two screws pop the assy off the back of the alternator to check.
• Weird guage problems (tach or mpg guage erratic, etc.) indicate a possible SI battery replacement needed. Very typical, and lots written on the subject.
• Dead SI batteries may also cause the Oil Service lights to be on at odd times. <$10 for batts, couple hundred for rebuilt board.
• If batt's are OK, lights are very easily reset, refer to FAQ's and/or reset tools, or, for the very brave, just ground pin 7 of the diagnostic connector, turn on the ignition (but don't start) for 15 seconds, turn it off, and you're done. Many will tell you this procedure is highly risky, but so is cutting vegetables with a dull knife - sheesh! no rocket science here. (15 pin version)
• Jump pins 11 to 14 for remote start.
• Headrest up/down dies. Easy fix, good FAQ's elsewhere. $0.
• Just an observation: window lift and sunroof switches were illuminated 'standard' in late '86 US cars on. Easy swap, wires already in place, as an easy upgrade. I got a set from Jason at Zionsville, very cool outfit (no affiliation, yada x 3) Also, they get mechanically sticky and electrically erratic if exposed to Armorall. Switches can be opened and cleaned.
• Fuse box has chronic, but easy problems. Fuse clips corrode, wirebrush 'em. Fuses corrode, replace 'em all. Connections inside the box can get erratic or hot. A real bear to troubleshoot.
• Several chronic problems show up as 'cutting out' at any speed, frequently the 'main' relay, sometimes the fuel pump relay, sometimes the position or timing sensors. Connections to the _underside_ of Fuse 6 can corrode and heat up.
• Several handy voltages to know, measured at the battery: 10.0v - voltage while cranking starter 12.3v - 50% charged battery, 'at rest' 12.7v - fully charged battery, 'at rest' 13.6v - minimum acceptable alternator output at idle 14.3v - maximum acceptable alternator output at revs Ref: Mark Calabrese article "In the Dark?"

  March, 1996 Roundel 9) General

• Don't believe a _dang_ thing a salesperson says, if there is not documentation behind it. "Changed the oil every 3K miles" if literally true means they _never_ changed the filter. Semantics? Maybe. The car tells the real story, a salesperson has a car to sell.
• Lots of exhaust replacement opinions, choose one you like. The E28 cats crack, but can be successfully welded for years.
• Water in the trunk is usually a bad (hardened and/or cracked) rubber gasket around the taillight assy's. Replace them both.
• Buy a Bentley manual, and an ETM (Electronic Troubleshooting Manual) if you are electrically astute.
• Check to see if it has the TRX tires. If so, you face one of the classic $$$ delimmas - discount asking price $400 if tires OK, $1000 if tires need replacement. Many details elsewhere.
• For an excellent treatment of all the E- and M- numbers, check: http://www.unixnerd.demon.co.uk/enumber.html, John Burns' page.